2002 prius - battery block 8 becomes weak - which cell?

It turns out not to be necessary to know which cell is bad, because you can only replace in groups of six cells anyway - that's how many NiMH cells are in one of the 7.2 volt rectangular modules that are assembled into your battery - 38 modules total (228 cells).

If you looked closely at the wiring, you've probably already seen that the computer only divides the battery into 19 blocks for voltage measurements - each block is two adjacent modules (or 12 cells). If it is detecting a problem in block 8, that would direct your attention to modules 15 or 16 - is that where you were looking?

What does Techstream say about the series resistance of the different blocks, in addition to their voltages?

-Chap

 

Maybe shuffle a few modules so those two end up in different blocks, and see what the ECU has to say about that?

-Chap

 

The module voltage difference is measured under load of discharge and charging at high currents (50/60 amps).
Also check with an ohm meter the sense wires from modules 15 and 16 back to the ECU connector. These break at the point where they join the eye terminal on the bus bars, and are very difficult to spot. A broken wire gives a false reading for that module pair.

John

 

When you say the sense wires on the terminals seem ok did you test or just look?
The modules are counted from the ECU end.

John

 

Did you move any of the modules around -- i. e. did you swap module 8 with module 15, e. g.?

Or did you just clean up all the terminals/contacts and put it back together?

 

Good to know, hopefully that is enough.

 

A little obscure, there is an "ini" (if memory serves me right) that can be edited to increase the duration of data recording. The default is ~240 seconds but a much larger value allows it to run long enough to get a good commute record.

Bob Wilson

 

The car only looks at the block level (2 modules). It's easiest to replace both modules when you have a bad block, and if suspect modules were in the middle of the pack best to move them to the "easy end" of the pack case you need to replace them again (and to help with heat dissipation since modules in the middle can run hotter than at the ends)

For those who cannot figure out which end of battery is which, If you look closely on the inside base of the gen1 battery enclosure there are numbers stamped into the case every 5 modules which help with orientation. There are 38 modules, each block is two modules so if "block 8" is bad you'll want to replace modules 15 & 16. There is no stamping on other Prius packs (Gen2 and 3 etc). You can also confirm which block is which by comparing sense wire color with wiring diagram.

 

Yes, your code could have been caused by dirty or corroded sensing wires, but it would not be my first guess.

With Techstream you can look at live battery data while under charge and discharge. To get to the the live data first run a health check, then click on the battery category, then data list. Weak module pairs will stand out with larger voltage swings. With this test you do not have to pay attention to both driving and Techstream. Static module voltage does not give a complete a picture of module health.

Charge test : Engine on, set parking brake, car in drive, step on gas and brake fully. Your car will just sit still and charge. Give it about thirty seconds to a minute. The weak module pair voltage will rise faster and higher than the rest.

Discharge test: Car on and warmed up, engine off, set parking brake, car in reverse, step on the brake, give it a little gas but not so much that the gas engine turns on. The car will sit still and discharge the battery. Give it about a minute. The weak module pairs will drop in voltage faster and farther.

Brad

 

Hi romanlutsk. How is the battery performing now after a couple months? We're there any symptoms before the errors popped up?